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APHY 201 Exam 1b
Ch. 3 Cell Structure and Genetic Control
| Question | Answer |
|---|---|
| how many nuclei do skeletal muscle cells have? | hundreds |
| the nucleus is enclosed by what structure, made of 2 membranes? | the nuclear envelope |
| the nuclear envelope has 2 membranes. what are they and what are their features? | the outer membrane of the nucleus is continuous with the rough ER and the inner membrane is fused to the outer by nuclear pore complexes, which allow small molecules and RNA to move into/out of the nucleus |
| what are the two steps that together are called genetic expression? | genetic transcription and genetic translation |
| what is the difference between genetic transcription and translation? | in transcription, the gene on the DNA is transcribed as messenger RNA which can leave the cell; in translation, the messenger RNA is then translated at the ribosome to assemble the proper amino acid sequence |
| know these terms in the order they go in genetic expression | DNA, transcription, transcription factors/RNA polymerase, pre-mRNA, spliceosome, mRNA, ribosome, translation, tRNA, amino acids, polypeptide, protein |
| what important DNA do nucleoli contain? | the nucleoli contain the DNA that codes for the production of ribosomal RNA, the DNA that makes the ribosomes |
| how many different genes are in the human genome? | believed to be about 20,000; not all of these code for proteins as some are transcribed into types of RNA |
| what is the name for all the proteins that are produced from the genome? | the proteome |
| how many proteins are produced in the human body? | more than 100,000 |
| how can a gene code for more than one protein? (...changing the recipe before cooking) | alternative splicing allows one precursor mRNA to be used to make multiple proteins: mRNA is altered after transcription by cutting and splicing different ways. exons are expressed (kept), introns are "thrown away" for intervening |
| what two actors join exons together in the process of RNA synthesis (specifically pre-mRNA modification)? | spliceosomes and snRNPs (small nuclear ribonucleoproteins) |
| how is it possible for a given group of many polypeptide chains to make different proteins? | proteins are made of polypeptide chains that can associate in different combinations, and protein modification can occur by adding a lipid, carbohydrate, or functional group (methyls, phosphoryls...) |
| what are the 3 ways a protein is modified post-translation? (...changing the ingredients at cooking) | methylation, phosphorylation, and/or cutting fabricated protein into small units |
| what is methylation? | adding a -CH3 group |
| what is phosphorylation? | adding a PO4^3- group |
| what is the difference between histones, nucleosomes, and chromatin? | histones are the spools, nucleosomes are the spool plus thread of DNA on it, chromatin is the collective name for the entire mixture of DNA and structural proteins (like histones) inside the nucleus; chromatin makes up chromosomes later |
| what is the charge on histones and why is that significant for DNA? | histones are positively charged and will interact with negatively charged DNA to cause spooling, creating nucleosomes |
| what are euchromatin and heterochromatin? | these are the two primary structural states that chromatin can take inside the nucleus (see further flashcards) |
| what is euchromatin (as opposed to heterochromatin)? | euchromatin is the looser form of chromatin--chemical changes in histones such as aceytlation highly allow molecules access to the DNA during gene expression |
| what is heterochromatin (as opposed to euchromatin)? | inactive regions are DEACETYLATED, and highly condensed; much of the DNA is inactive, so these genes are not expressed! |
| what is methylation and acetylation and what does it have to do with chromatin? | acetylation is almost always an activation signal; methylation acts as a silencing signal. cells all contain the exact same blueprint; the only reason a skin cell acts like a skin cell is because of its unique pattern of acetylation and methylation |
| what is the term for "DNA-directed RNA synthesis" and why? | transcription, because it involves start and stop regions for a gene, as well as involving promoters (non-gene regions whose DNA tells enzymes where to begin); transcription factors (TFs) bind to the promoter to begin transcription |
| what is RNA polymerase doing mechanically between the base pairs of DNA as it forms precursor messenger RNA (pre-mRNA) that detaches from the DNA template? | it's breaking hydrogen bonds |
| what are the 4 types of RNA? (know their roles in the process of transcription and translation) | pre-mRNA (precursor messenger), mRNA (messenger), tRNA (transfer), rRNA (ribosomal) |
| which type of RNA is made directly by transcription? | pre-mRNA (precursor messenger RNA) |
| which type of RNA used to be pre-RNA but is now modified? it contains the code to make a specific protein. | mRNA (messenger RNA) |
| which type of RNA carries amino acids to mRNA for translation? | tRNA (transfer RNA) |
| which type of RNA forms ribosomes together with protein? it is the site of translation and acts as an enzyme. | rRNA (ribosomal RNA) |
| when is pre-mRNA altered, before or after it leaves the nucleus? how is it altered? | before it leaves the nucleus as messenger RNA (mRNA), pre-mRNA is altered by spliceosomes, keeping exons and splicing out intervening introns |
| what are introns known as intervening? | introns may regulate the expression of the area that do code for protein |
| what is the important main point of RNA interference? | that RNA molecules that don't code for proteins may prevent some mRNA molecules from being translated--used in volume control or viral defense. the expression of at least 30% of genes is regulated in this way. |
| what are the 3 types of interfering/silencing RNAs? | short interfering (siRNA)--double-stranded, micro interfering (miRNA)--single-stranded, and circular RNA (circRNA) |
| describe siRNA? | small interfering RNA (siRNA) often comes from outside the cell (like a virus) or from long double-stranded RNA that leaves the nucleus. it is highly specific and targets just one exact mRNA sequence. |
| what role does Dicer play with siRNA? | w/o Dicer, cell would have long, useless strands of siRNA precursor. Dicer acts as the critical bridge: cuts it to the exact operational length, and hands it off to the cellular security team so gene silencing can actually happen |
| describe miRNA? | micro interfering RNA (miRNA) is a class of tiny, single-stranded, non-coding RNA molecules that doubles over in hairpin loops of double-stranded RNA. MADE FROM INTRONS removed from pre-mRNA |
| describe circRNA? | circular RNA (circRNA) is a type of single-stranded RNA that forms a covalently closed continuous loop rather than a standard open-ended structure, protecting it from rapid degradation. MADE FROM EXONS |
| what is important about circRNA relative to miRNA? | each circRNA molecule has numerous binding sites for copies of a particular miRNA. within a RISC particle, this binding serves as a sponge--they inhibit the inhibitory miRNA, allowing protein production to go on |
| how does silencing machinery (RISC) find its target, and how does it physically block the assembly line? | the RISC complex carries siRNA and miRNA around the cell so they can bind to single-stranded mRNA where they are complementary. this creates a block so that tRNA can't bring amino acids to mRNA, and translation is prevented. |
| what is CRISPR-Cas9? | CRISPR-Cas9 is a gene-editing technology that is more specific than gene inactivation through RNA inhibition via microRNA. CRISPR-Cas9 employs a guide RNA (gRNA) to find a target gene, then a nuclease enzyme (Cas9 is a well-known one) cuts the DNA |
| what are the applications of CRISPR-Cas9? | remove specific genes, inactivate genes without removing them, and activate specific genes (rather than repress them) |
| what pieces of DNA or RNA does Dicer act on? | pre-miRNAs, siRNAs, and Transfer RNA Fragments (tRFs) |
| where are newly formed proteins made when they're destined to leave the cell? | rough ER aka granular ER |
| how is the newly formed (outgoing) protein first attracted to the lipid portion of the membrane of the RER? | the first 30 or so amino acids are hydrophobic, so they're attracted to the lipid portion of the RER membrane. however, this hydrophobic leader sequence is removed later, and other portions may be removed or added (at the cisternae?) |
| after the RER, where are secretory proteins sent? | the Golgi complex, where proteins may be further modified (--> glycoproteins), separated according to destination, and packaged and shipped in vesicles to their destinations |
| what role does protein degradation play in protein synthesis and secretion? | clears out misfolded proteins, reclaims amino acids for new synthesis, and removes unneeded secretory proteins to prevent toxic buildup and ensure homeostasis |
| the lysosomes play a role in protein degradation. specificaly, what "ase" digests proteins? | protease(s) |
| what about proteins outside the lysosomes? what happens to them? | proteins outside the lysosomes are tagged by a molecule called ubiquitin, which marks them for degradation by a proteasome. ubiquitin may also tag membrane proteins and organelles for destruction |
| DNA replication involves what 2 types of enzymes? | DNA helicases and DNA polymerase, the latter of which attaches complementary nucleotides to the exposed strand |
| true or false, in DNA replication, two new molecules are being made from the original one, each with half old and half new DNA | true |
| what is semiconservative replication? | the standard method of DNA replication in which the original double helix unwinds, and each strand serves as a template for a new strand |
| what are the phases of interphase? | G1, S, and G2; then mitosis follows interphase |
| nuclear division is another name for what? | mitosis |
| cytokinesis is another name for what? | cell division |
| which cyclin moves the cell through G1 of interphase? | cyclin D (overactivity of which has been implicated in some cancers) |
| what is the name of the transcription factor that can stall a gene at the G1/S checkpoint, repair DNA damage or promote apoptosis? | p53 is the name of the transcription factor. fun fact, "knocked out" mice with their p53 gene removed are used to study cancer and apoptosis |
| if a cell does not divide, it remains in a modified G1 phase its whole life. what phase is this known as? | G0 |
| at what phase does DNA replication occur if a cell is going to divide? | S phase (synthesis) is the phase wherein DNA replication is performed if a cell will divide |
| at what phase do chromosomes START to condense? | G2 phase (Gap 2) |
| what does a chromosome consist of? | two strands called sister chromatids, joined by a centromere |
| what are the 2 types of cell death, and what is the difference between them? | necrosis happens when cell dies pathologically due to deprivation of blood supply, while apoptosis is programmed cell death performed by caspases enzymes |
| describe extrinsic and intrinsic apoptosis? | extrinsic: "death ligands" attach to the cell and mark it for destruction; intrinsic: intercellular signals trigger death due to DNA damage, cancer, infection, or oxidative stress |
| in which phases do chromosomes start and finish condensing, becoming visible? | chromosomes start to condense at G2 of interphase, and finish condensing in prophase |
| recognize for multiple choice: what happens in prophase? | chrosomes become visible as they finish condensing, nuclear membrane and nucleolus disappear, centrioles move apart, spindle fibers form |
| what is the role of the centrosome in mitosis? | nucleate and organize the microtubules that form the mitotic spindle |
| how many centrioles are at the center of the centrosome? | 2 |
| what is the role of the centrosome relative to the spindle fibers? | the centrosome anchors the spindle fibers, which form from the pericentriolar materials around the centrioles and attach to the centromere of the replicated sister chromatids. other tubules cause the cleavage furrow for cytokinesis |
| what happens to the centrosome in nondividing cells? in ciliated cells? | in nondividing cells, the centrosome migrates to the plasma membrane and forms the nonmotile primary cilium; in ciliated cells, hundreds of centrosomes form and become the basal bodies of the cilia |
| what is the role of telomeres in cell division? | during cell division, they function as protective caps (similar to the plastic tips on shoelaces) that prevent chromosomes from fraying, degrading, or fusing with one another |
| true or false, a cell keeps dividing after its telomeres are damaged | false, at least in a healthy cell where p53 is active |
| each time DNA is replicated, a little more telomere is lost; loss of the ability to divide may be due to the loss of telomeres. bone marrow divides indefinitely, and has which enzyme that replicates the telomere? | telomerase |
| when telomeres are damaged, p53 is activated. what 3 processes does p53 induce? | cell cycle arrest, senescence (aging), and apoptosis |
| distinguish between hyperplasia and hypertrophy? | hyperplasia is growth due to increase in |
| which meiotic phase swaps parts of homologous chromosomes (crossing over)? shuffles maternal and paternal chromosomes? | metaphase I |
| how is telophase I different from mitotic telophase? | telophase I (of meiosis) differs from mitotic telophase because it separates homologous chromosomes instead of sister chromatids |
| true or false, crossing-over and shuffling of chromosomes in metaphase I results in genetic recombination and genetic diversity | true |
| meiosis II procees like mitosis with phases prophase II through telophase II, but what's different? | the key difference is ploidy: meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells. additionally, meiosis II results in four genetically unique cells, unlike mitosis which yields two identical clones |
| which results in 4 cells with 23 chromosomes each, meiosis I or II? | meiosis II |
| (starred) what occurs in prophase I? | chromosomes appear double-stranded; each chromatid strand contains duplicate DNA joined by centromere; homologous chromosomes pair up |
| (starred) what happens in metaphase I? | homologous chromosome pairs line up at equatorial plate; meiotic spindle is complete |
| (starred) what happens in anaphase I? | homologous chromosomes separate; the two members of a homologous pair move to opposite poles |
| (starred) what happens in telophase I? | cytoplasm divides to produce two haploid cells |
| (starred) what happens in prophase II? | chromosomes appear, each containing two chromatids |
| (starred) what happens in metaphase II? | chromosomes line up single file along the equatorial plate as spindle formation is completed |
| (starred) what happens in anaphase II? | centromeres split and chromatids move to opposite poles |
| (starred) what happens in telophase II? | cytoplasm divides to produce 2 haploid cells from each of the haploid cells formed at telophase I |
| what is significant about epigenetic inheritance in your notes? | silenced genes are passed to daughter cells during mitosis and meiosis without a change in DNA base sequence, including the next generation in sperm and ova! (food deprivation) |
| what are the 2 mechanisms of epigenetic inheritance? | 1) posttranslational modifications of histone proteins 2) methylation (silencing signal) of cytosine bases in DNA that precede guanine |
| recognize for multiple choice: problems with epigenetic inheritance contribute to which disorders? | cancer, fragile X syndrome, and systemic lupus erythematosus |
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